Rollup merge of #119216 - weiznich:use_diagnostic_namespace_in_stdlib, r=compiler-errors

Use diagnostic namespace in stdlib

This required a minor fix to have the diagnostics shown in third party crates when the `diagnostic_namespace` feature is not enabled. See https://github.com/rust-lang/rust/pull/119216/commits/5d63f5d8d1a72167c1d5242b2e1ed5b7259fd526 for details. I've opted for having a single PR for both changes as it's really not that much code. If it is required it should be easy to split up the change into several PR's.

r? `@compiler-errors`

1 files changed, 1 insertions, 3 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index 52f91d282f0..c9e8b30c4c4 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -521,7 +521,7 @@ impl<'tcx> OnUnimplementedDirective {
     pub fn of_item(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> Result<Option<Self>, ErrorGuaranteed> {
         if let Some(attr) = tcx.get_attr(item_def_id, sym::rustc_on_unimplemented) {
             return Self::parse_attribute(attr, false, tcx, item_def_id);
-        } else if tcx.features().diagnostic_namespace {
+        } else {
             tcx.get_attrs_by_path(item_def_id, &[sym::diagnostic, sym::on_unimplemented])
                 .filter_map(|attr| Self::parse_attribute(attr, true, tcx, item_def_id).transpose())
                 .try_fold(None, |aggr: Option<Self>, directive| {
@@ -592,8 +592,6 @@ impl<'tcx> OnUnimplementedDirective {
                         Ok(Some(directive))
                     }
                 })
-        } else {
-            Ok(None)
         }
     }